Issue 26

G. Fargione et alii, Frattura ed Integrità Strutturale, 26 (2013) 143-155; DOI: 10.3221/IGF-ESIS.26.14

Figure 9 : Results of FE Analysis.

The diagram of the Fig. 9 reports the material yield load variation with respect to the steam temperature. In the same graph it has been reported the Von Mises maximum stress value reached in the middle section of the tie rod changing the local temperature and the stress deviation from proportionality at high temperatures. It can be observed that at a 350 °C temperature the stress value is equal to the material yield stress and with a temperature of 450 °C (equal to the steam come out from the flange) the stress is 40% over the material yield stress. Experimental Analysis In order to determine the mechanical characteristics of the material both static and fatigue tests have been performed. As it has been already said, the static tests have been carried out on 2 of the eight specimens, one belonging to the tie rod A (specimen 1) and another of the tie rod B (specimen 2). The tests have been done using an electrohydraulic machine INSTRON (R) 8501 with a fixed crossrate equal to 1 mm/min. The test has been accompanied by the detection and the acquisition of the surface temperature of the specimens using an IR camera FLIR (R) 3000 with a frame rate of 1 Hz. The Fig. 10 reports the deformation stress graph of one of the tested specimen 1. In the same figure it has been reported the temperature trend of the hottest area of the specimen surface showing the unit deformation of the specimen itself. The temperature trend has been deduced examining the following images obtained during the traction test. For a better understanding, in Fig. 11 it has been reported the first part of the temperature curve vs strain (till ε = 0.04) of specimen 1.

Figure 10 : Stress vs strain curve and temperature trend of specimen 1 mono axial static test.

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